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Nanostructured and organic semiconductors form the basis of a new generation of prospective materials for solar cell fabrication. The efficiency of solar cells crucially depends on the speed of long-range charge carrier transport and the understanding of the transport mechanisms in the mentioned materials is a key knowleged for its improvements. We used time-resolved terahertz spectroscopy as a contact-free probe of ultrafast carrier transport. The technique permits to access easily the complex conductivity in the terahertz spectral range with subpicosecond time resolution. The experiments were carried out in a concert with numerical simulations of the conductivity spectra and this allowed us to elucidate the transport mechanisms in a number of complex materials. Celý text >>
Metamaterials are artificially created composite periodic structures with a unit cell much smaller than the targeted wavelength of the radiation. These materials may exhibit electromagnetic properties not found in nature. It appear that by using a suitable combination of composite constituents it is possible to conceive for example an “invisibility cloak” or plates with a negative refractive index allowing one to overcome the diffraction limit in the optical imaging. However, these properties can be used in a narrow spectral range only restricted by the width of very sharp magnetic resonances (in permeability). For this reason we proposed and experimentally realized a metamaterial with a tunable range of negative effective permeability in the terahertz spectral range (0.2 – 0.36 THz) [H. Němec et al., Phys. Rev. B 79, 241108 (2009)]. Celý text >>
We investigate materials with globally or locally broken center of inversion, such as piezoelectric, ferroelectric, antiferroelectric, relaxor or incommensurate dielectrics in form of crystals, ceramics, films as well as complex nanostructures. The team focuses on developing preparation methods, by characterization of structural phase transitions by calorimetric, structural and nonlinear optic methods, and by theoretical modeling of their physical properties.
Celý text >>We focus on study of dielectric spectra of ferroelectrics in the form of single crystals, ceramics, thin films and multilayers in a very broad spectral and temperature range (1 mHz – 150 THz, 5 – 950 K).
Celý text >>Investigations of novel liquid crystals with dipolar order, understanding of their phase diagram, topological defects and low frequency relaxations responsible for dielectric behavior.
Celý text >>Terahertz (THz) radiation lies in the frequency range between the infrared and microwaves, i.e. between 100 GHz and 10 THz. These waves are able to excite soft polar phonons in solids, vibrations of larger chains in biomolecules, to induce plasma oscillations of free charge carriers with concentrations of ~1014–1018 cm-3 and to interact with carriers localized in nanoparticles. Due to the lack of bright sources and sensitive detectors the THz spectroscopic applications about 20 years ago concerned mainly the astronomy and analytical science. Recent technological innovations in photonics and nanotechnology have lead to a dramatic increase in the interest of the scientific and industrial community in the THz research and applications.
Celý text >>Copyright © 2008, Fyzikální ústav AV ČR, v. v. i.
